The overall aim of our research program is to contribute toward an understanding of the structure and biological activity of immunoglobulins. In line with this overall objective we are carrying out the following projects: 1. The structure and properties of an unusual myeloma protein. The crystallizable IgG1 myeloma protein "Dob" apparently has a limited deletion of the hinge region of the heavy chain. We are now carrying on studies to determine the exact location and extent of the deletion. We will then examine the physical-chemical properties of the molecule to determine the effects of the absence of the hinge region on the conformation and biological properties of this protein. 2. The immune response in tadpoles and frogs. We are studying the immune system in amphibia from several points of view. These include: (1) The isolation and characterization of the immunoglobulins in the adult bullfrog with emphasis on the relation of these proteins to the immunoglobulins of mammals. (2) An analysis of the development of the various Ig classes in the tadpoles and of the possible regulation of this development by specific immunization procedures. (3) A study of cellular immunity in frogs and tadpoles. (4) studies directed at the question: Are adult frogs tolerant of fetal proteins (e.g., hemoglobin) that were produced during the tadpole stage? (5) An investigation of the complement system in this species. 3. Cross reactions and serological specificity. We will investigate the changing patterns of cross-reactivity of antisera during the course of the immune response. In particular, we will determine whether any of the antibodies in an immune serum bind more strongly to a cross-reacting antigen than to the immunogen.